Secrecy can be sexy. It's essential to any good mystery novel. But there should be no mystery surrounding the pay of top public officials. In October 2008 I made freedom of information requests to every police force in the country seeking the full extent of chief constables' perks and pay. I'd heard rumours top cops weren't just getting top salaries but all sorts of other benefits, from grace and favour homes to chauffeur-driven SUVs and private health insurance.

These perks may be perfectly acceptable – after all, it's a tough job. What is not acceptable is the vault-like secrecy in which they are awarded. Several forces told me their chiefs refused bonuses out of principle. But of all those who accepted them only one force, North Wales, fully disclosed the amount.

Why the secrecy? The official reason is that disclosure would be an invasion of chiefs' privacy. Here's the response given by City of London police: "We do not believe that disclosing the exact value of the commissioner's bonus will add significantly to the public interest. By contrast, given that the commissioner has refused consent to disclose and has a reasonable expectation that the exact value of his performance-related payment will remain confidential, we believe that disclosure would be prejudicial to the commissioner's rights and freedoms or legitimate interests."

What about the rights and freedoms of taxpayers to know how their money is spent? What about knowing the criteria on which these bonuses are awarded? Are chiefs paid for achieving political goals? For decreasing crime statistics? For increasing the number of ethnic minority officers? We just don't know.

Spratt sought the compensation package of Northern Ireland's outgoing chief constable Hugh Orde, who is now president of the Association of Chief Police Officers. He managed to unearth a compensation package that included rent-free living in a £600,000 luxury home (purchased at taxpayer expense) along with the payment of all utility bills, including phone bills, electricity, rates, heating and property maintenance. This is in addition to a salary of £183,954 plus an annual bonus of up to 15% of salary. Other extras included £360 a year for broadband, £600 for private healthcare, and membership fees for Acpo and the Chief Police Officers' Staff Association, estimated to be £1,000 annually. Another £8,294 was claimed for oil and £13,413 for rates, while £33,904 was spent to repair "defective combined drainage system" and to replace the kitchen.

Now you might think that a member of the police board (the Northern Irish equivalent of a police authority) would know exactly what comprises a top cop's compensation package, as the board approves it. Not so. Spratt tells me that when you have a £1.2bn budget "you can't really keep track".

"What you're presented with are accounts that are, well I wouldn't exactly call them basic, but they're not going into any great detail, and it's only when you start probing into the detail that you find these things out. I wanted to know what I was signing my name to." If only more police authority members did the same. As a former chief negotiator on police pay, Spratt thought he had a good idea what was on offer, but was "completely surprised" at the extent.

Where are these packages set? Spratt is finding that difficult to pin down. He's been told they're set by the Association of Police Authorities but its acting executive, Tania Eagle, told me that's not the case. "It's very unusual for one agency to be fully responsible for policy."

That's the problem. We need clear lines of accountability. We need to know who's in charge of setting and approving these packages and we need to get them out in the open. Even Acpo is starting to agree. Spokesman Andrea Newman says: "Acpo is of the view that chief officers should be open and transparent about their remuneration and should be open to scrutiny – but disclosure is a matter for individual chief constables."

If these payouts are to be respected then chief constables must come clean about their pay. Secrecy feeds suspicion that these perks are based on politics and boys' club favouritism rather than effective policing.